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| United States Patent |
5,206,196
|
|
Nakano
, et al.
|
April 27, 1993
|
Catalyst for purifying exhaust gas
Abstract
A catalyst for purifying an exhaust gas to remove nitrogen oxides, carbon
monoxide and hydrocarbons from an oxygen-rich exhaust gas containing
nitrogen oxides, carbon monoxide and hydrocarbons comprising (i) a zeolite
having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least 15 and (ii)
(a) cobalt, (b) a rare earth metal and (c) silver, or nickel and/or zinc,
or platinum and/or manganese, or copper and/or rhodium, incorporated
thereinto.
| Inventors:
|
Nakano; Masao (Hikari, JP);
Eshita; Akinori (Shinnanyo, JP);
Sekizawa; Kazuhiko (Shinnanyo, JP)
|
| Assignee:
|
Tosoh Corporation (Shinnanyo, JP)
|
| Appl. No.:
|
805611 |
| Filed:
|
December 12, 1991 |
Foreign Application Priority Data
| Dec 18, 1990[JP] | 2-411258 |
| Dec 18, 1990[JP] | 2-411259 |
| Dec 18, 1990[JP] | 2-411260 |
| Dec 18, 1990[JP] | 2-411261 |
| Current U.S. Class: |
502/73; 502/65 |
| Intern'l Class: |
B01J 029/10 |
| Field of Search: |
502/65,73,71,77
423/239
|
References Cited
| Foreign Patent Documents |
| 45054 | Feb., 1982 | EP | 502/71.
|
| 0362966 | Apr., 1990 | EP.
| |
| 0415410 | Mar., 1991 | EP.
| |
| 0434063 | Jun., 1991 | EP.
| |
| 50-55575 | May., 1975 | JP | 423/239.
|
| 52-30771 | Mar., 1977 | JP | 423/239.
|
| 2201647 | Sep., 1987 | JP | 423/239.
|
| 63-283727 | Nov., 1988 | JP.
| |
| 1-130735 | May., 1989 | JP.
| |
| 2-251247 | Oct., 1990 | JP | 502/77.
|
Primary Examiner: Dees; Carl F.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt
Claims
We claim:
1. A catalyst for purifying an exhaust gas to remove nitrogen oxides,
carbon monoxide and hydrocarbons from an oxygen-rich exhaust gas
containing nitrogen oxides, carbon monoxide and hydrocarbons comprising
(i) a zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least
15 and (ii) (a) cobalt, (b) a rare earth metal and (c) silver,
incorporated therein.
2. A catalyst for purifying an exhaust gas as claimed in claim 1, wherein
said zeolite has the composition:
xM.sub.2/n O.multidot.Al.sub.2 O.sub.3 .multidot.ySiO.sub.2
.multidot.zH.sub.2 O
wherein n is a valency of the cation, x is 0.8 to 2, y is at least 2, and z
is at least 0.
3. A catalyst for purifying an exhaust gas as claimed in claim 1, wherein
the contents of the cobalt and the rare earth metal are 0.1 to 1.5 times
and 0.1 to 1 time, respectively, in terms of a mole ratio to the alumina
in the zeolite.
4. A catalyst for purifying an exhaust gas as claimed in claim 1, wherein
the content of silver is 0.05 to 2 times and the total content of cobalt,
rare earth metal and silver is 1.0 to 2.5 times, in terms of a mole ratio
to the alumina in the zeolite.
5. A catalyst for purifying an exhaust gas to remove nitrogen oxides,
carbon monoxide and hydrocarbons from an oxygen-rich exhaust gas
containing nitrogen oxides, carbon monoxide and hydrocarbons, comprising
(i) a zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least
15 and (ii) (a) cobalt and (b) a rare earth metal and (c) at least one
metal selected from the group consisting of nickel and zinc, incorporated
therein.
6. A catalyst for purifying an exhaust gas as claimed in claim 5, wherein
said zeolite has the composition:
xM.sub.2/n O.multidot.Al.sub.2 O.sub.3 .multidot.ySiO.sub.2
.multidot.zH.sub.2 O
wherein n is a valency of the cation, x is 0.8 to 2, y is at least 2, and z
is at least 0.
7. A catalyst for purifying an exhaust gas as claimed in claim 5, wherein
the contents of the cobalt and the rare earth metal are 0.1 to 1.5 times
and 0.1 to 1 time, respectively, in terms of a mole ratio to the alumina
in the zeolite.
8. A catalyst for purifying an exhaust gas as claimed in claim 5, wherein
the content of nickel or zinc is 0.05 to 2 times and the total content of
cobalt and rare earth metal and nickel and/or zinc is 1.0 to 2.5 times, in
terms of a mole ratio to the alumina in the zeolite.
9. A catalyst for purifying an exhaust gas to remove nitrogen oxides,
carbon monoxide and hydrocarbons from an oxygen-rich exhaust gas
containing nitrogen oxides, carbon monoxide and hydrocarbons comprising
(i) a zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least
15 and (ii) (a) cobalt and (b) a rare earth metal and (c) at least one
metal selected from the group consisting of platinum and manganese,
incorporated therein.
10. A catalyst for purifying an exhaust gas as claimed in claim 9, wherein
said zeolite has the composition:
xM.sub.2/n O.multidot.Al.sub.2 O.sub.3 .multidot.ySiO.sub.2
.multidot.zH.sub.2 O
wherein n is a valency of the cation, x is 0.8 to 2, y is at least 2, and z
is at least 0.
11. A catalyst for purifying an exhaust gas as claimed in claim 9, wherein
the contents of the cobalt and the rare earth metal are 0.1 to 1.5 times
and 0.1 to 1 time, respectively, in terms of a mole ratio to the alumina
in the zeolite.
12. A catalyst for purifying an exhaust gas as claimed in claim 9, wherein
the content of platinum or manganese is 0.05 to 1.5 times and the total
content of cobalt and rare earth metal and platinum and/or manganese is
1.0 to 2.5 times, in terms of a mole ratio to the alumina in the zeolite.
13. A catalyst for purifying an exhaust gas to remove nitrogen oxides,
carbon monoxide and hydrocarbons from an oxygen-rich exhaust gas
containing nitrogen oxides, carbon monoxide and hydrocarbons comprising
(i) a zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least
15 and (ii) (a) cobalt and (b) a rare earth metal and (c) at least one
metal selected from the group consisting of copper and rhodium,
incorporated therein.
14. A catalyst for purifying an exhaust gas as claimed in claim 13, wherein
said zeolite has the composition:
xM.sub.2/n O.multidot.Al.sub.2 O.sub.3 .multidot.ySiO.sub.2
.multidot.zH.sub.2 O
wherein n is a valency of the cation, x is 0.8 to 2, y is at least 2, and z
is at least 0.
15. A catalyst for purifying an exhaust gas as claimed in claim 13, wherein
the contents of the cobalt and the rare earth metal are 0.1 to 1.5 times
and 0.1 to 1 time, respectively, in terms of a mole ratio to the alumina
in the zeolite.
16. A Catalyst for purifying an exhaust gas as claimed in claim 13, wherein
the content of copper or rhodium is 0.05 to 1.5 times and the total
content of cobalt and rare earth metal and copper and/or rhodium is 1.0 to
2.5 times, in terms of a mole ratio to the alumina in the zeolite.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalyst for purifying an exhaust gas to
remove nitrogen oxides, carboxy monoxide and hydrocarbons contained in an
exhaust gas discharged, for example, from internal combustion engines of
automobiles. More specifically, it relates to a catalyst for removing
nitrogen oxides contained in an oxygen-rich exhaust gas.
The term "oxygen-rich exhaust gas" used in the present invention is
intended to mean an exhaust gas containing oxygen in an amount exceeding
the amount of oxygen necessary for completely oxidizing carbon monoxide
and hydrocarbons contained in the exhaust gas.
2. Description of the Related Art
Nitrogen oxides, carbon monoxide and hydrocarbons, which are toxic
substances contained in an exhaust gas discharged from internal combustion
engines, are removed, for example, through the use of a three-way catalyst
comprising Pt, Rh, Pd, etc., supported on a carrier material. In the case
of an exhaust gas discharged from diesel engines, however, no effective
catalyst exists for removing nitrogen oxides because the exhaust gas
contains a large amount of oxygen, and thus a purification of the exhaust
gas by a catalyst has not been realized.
In recent gasoline engines, a lean burn combustion is used for lowering the
fuel consumption and reducing the amount of exhausted carbon dioxide gas,
but an exhaust gas from this lean burn gasoline engine comprises an
atmosphere containing an excessive amount of oxygen, and therefore, it is
impossible to apply the above-mentioned conventional three-way catalyst,
and thus a method of removing toxic components from the exhaust gas has
not been put to practical use.
Examples of the method of removing particularly nitrogen oxides in an
exhaust gas containing an excessive amount of oxygen include that wherein
a reducing agent, such as ammonia, is added, and that wherein the nitrogen
oxides are absorbed in an alkali, to remove same. These methods are not
effective for automobiles, which are a moving nitrogen oxides source, and
thus the application thereof is limited.
Recently it has been reported that a zeolite catalyst subjected to an ion
exchange with a transition metal can remove nitrogen oxides in an exhaust
gas containing an excessive amount of oxygen without the addition of a
special reducing agent such as ammonia. For example, Japanese Unexamined
Patent Publication (Kokai) Nos. 63-283727 and 1-130735 propose a catalyst
which can selectively reduce nitrogen oxides even in an exhaust gas
containing an excessive amount of oxygen and can remove minor amounts of
reducing agents such as unburnt carbon monoxide and hydrocarbons.
The activity of the above-mentioned catalysts proposed in the art, however,
is remarkably deteriorated when the catalyst is used at a high temperature
for a long time, and thus it is necessary to improve the durability and
catalytic performance thereof.
Accordingly, to solve the above-described problems, a catalyst for
purifying an exhaust gas comprising a zeolite having an SiO.sub.2
/Al.sub.2 O.sub.3 mole ratio of at least 15, and incorporated therein,
cobalt and a rare earth metal has been proposed (see Japanese Patent
Application No. 2-149203).
Although the exhaust gas purification catalyst proposed in Japanese Patent
Application No. 2-149203 has an improved durability, the temperature
region in which the nitrogen oxides can be removed is relatively narrow.
Therefore, a higher capability of removing nitrogen oxides in a broader
temperature region, particularly at a low temperature, is required from a
catalyst for purifying an exhaust gas discharged, in particular, from
automobiles.
SUMMARY OF THE INVENTION
Accordingly, the objects of the present invention are to eliminate the
above-mentioned disadvantages of the prior art and to provide a catalyst
for purifying an exhaust gas catalyst which is capable of simultaneously
removing nitrogen oxides, carbon monoxide and hydrocarbons from an exhaust
gas discharged from, for example, internal combustion engines of
automobiles, and is less susceptible to thermal deterioration and has a
high catalytic activity.
Other objects and advantages of the present invention will be apparent from
the following description.
The present inventors have made extensive and intensive studies into the
above-mentioned problems, and as a result, found that the incorporation of
any one of
(1) silver,
(2) nickel and/or zinc,
(3) platinum and/or manganese, and
(4) copper and/or rhodium,
in the above-mentioned catalyst for purifying an exhaust gas comprising a
zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of at least 15,
and incorporating therein cobalt and a rare earth metal, improves the
capability thereof of removing nitrogen oxides, and thus completed the
present invention.
Accordingly, the present invention provides a catalyst for purifying an
exhaust gas to remove nitrogen oxides, carbon monoxide and hydrocarbons
from an oxygen-rich exhaust gas containing nitrogen oxides, carbon
monoxide and hydrocarbons comprising a zeolite having an SiO.sub.2
/Al.sub.2 O.sub.3 mole ratio of at least 15, and incorporated thereinto,
cobalt and a rare earth metal and any one of
(1) silver,
(2) nickel and/or zinc,
(3) platinum and/or manganese, and
(4) copper and/or rhodium.
The present invention also provides a method of removing nitrogen oxides,
carbon monoxide and hydrocarbons contained in an exhaust gas by bringing
the catalyst for purifying an exhaust gas into contact with a combustion
waste gas containing nitrogen oxides, carbon monoxide and hydrocarbons.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in more detail.
The catalyst for purifying an exhaust gas according to the present
invention comprises a zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 mole
ratio of at least 15, and incorporated thereinto, the above-described
metals.
The above-mentioned zeolite generally has the following composition:
xM.sub.2/n O.multidot.Al.sub.2 O.sub.3 .multidot.ySiO.sub.2
.multidot.zH.sub.2 O
wherein n is a valency of the cation, x is 0.8 to 1.2, y is at least 2, and
z is at least 0 (zero). In the zeolite used in the present invention, the
SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio is preferably at least 15. There is
no particular limitation of the upper limit of the SiO.sub.2 /Al.sub.2
O.sub.3 mole ratio, but when the SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio is
less than 15, the heat resistance and durability of the zeolite per se are
low, and thus the heat resistance and durability of the catalyst are
unsatisfactory. The SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio is more
preferably about 15 to 1000.
The zeolite constituting the catalyst of the present invention may be a
naturally occurring zeolite or a synthetic zeolite. There is no particular
limitation of the method of producing the zeolite. Representative examples
of the zeolite used in the present invention include ferrierite, Y, ZSM-5,
ZSM-11, ZSM-12 and ZSM-20. These zeolites per se may be used as the
catalyst of the present invention, or used after treatment with an
ammonium salt, a mineral acid or the like for an ion exchange to form an
NH.sub.4 or H type zeolite.
The zeolite used in the present invention contains (a) cobalt, (b) rare
earth metal and (c) any one of
(1) silver,
(2) nickel and/or zinc,
(3) platinum and/or manganese, and
(4) copper and/or rhodium.
There is no particular limitation of the method of incorporating the
above-mentioned metals into the zeolite, and in general, the
above-mentioned metals can be incorporated by an ion exchange method, an
impregnation method, and an evaporation-to-dryness method through the use
of a water soluble salt. The above-mentioned metals may be incorporated at
one time, or may be successively incorporated.
When incorporating the above-mentioned metals in the zeolite, the
concentration of individual metal ions in the aqueous solution can be
properly selected depending upon the intended percentage ion exchange of
the catalyst. Examples of the rare earth metal ions include La, Ce, Pr, Nd
and Y. The above-mentioned metal ions may be used in a soluble salt, and
suitable examples of the soluble salt include nitrate, acetate, oxalate
and chloride.
Regarding the contents of the individual metals in terms of mole ratio to
the alumina in the zeolite, the contents of cobalt and rare earth metal
are preferably 0.1 to 1.5 times more preferably 0.2 to 1.4 times and 0.1
to 1 time, more preferably 0.2 to 1.0 time, respectively. Further,
preferably;
1) the content of silver is 0.05 to 2 times, more preferably 0.1 to 1.8
times and the total content of cobalt, rare earth metal and silver is 1.0
to 2.5 times, more preferably 1.0 to 2.3 times,
2) the content of nickel or zinc is 0.05 to 2 times, more preferably 0.1 to
1.8 times, and the total content of cobalt and rare earth metal and nickel
and/or zinc is 1.0 to 2.5 times, more preferably 1.0 to 2.3 times,
3) the content of platinum or manganese is 0.05 to 1.5 times, more
preferably 0.1 to 1.4 times, and the total content of cobalt and rare
earth metal and platinum and/or manganese is 1.0 to 2.5 times, more
preferably 1.0 to 2.3 times, and
4) the content of copper or rhodium is 0.05 to 1.5 times, more preferably
0.1 to 1.4 times, and the total content of cobalt and rare earth metal and
copper and/or rhodium is 1.0 to 2.5 times, more preferably 1.0 to 2.3
times.
The sample containing the above-described metals is generally used after
solid-liquid separation, washing and drying, and if necessary, can be used
after calcination.
The catalyst for purifying an exhaust gas according to the present
invention may be used after mixing with a binder, such as a clay mineral,
and then molding. Alternatively, the zeolite may be previously molded, and
the above-mentioned metals may be incorporated into the molding. Examples
of the binder used in molding of the zeolite include clay minerals such as
kaolin, attapulgite, montmorillonite, bentonite, allophane and sepiolite,
silica and alumina. Alternatively, the catalyst may be a binder-less
zeolite molding directly synthesized without the use of a binder. Further,
the zeolite may be wash-coated onto a honeycomb-structured base material
made of cordierite, a metal or the like.
The nitrogen oxides, carbon monoxide and hydrocarbons contained in an
oxygen-rich exhaust gas can be removed by bringing the exhaust gas into
contact with the exhaust gas purification catalyst according to the
present invention.
Specific examples of such an exhaust gas include exhaust gases discharged,
for example, from the internal combustion engines of automobiles,
particularly exhaust gases produced at a high air/fuel ratio (i.e., in the
lean burn region).
There is no particular limitation in the operating conditions of the
catalyst according to the present invention, but the preferable
temperature is 100.degree. C. to 900.degree. C., more preferably
150.degree. C. to 800.degree. C. and the preferable space velocity is
1,000 to 500,000 hr.sup.-1. The "space velocity" means a value of a gas
flow rate (cc/hr) divided by a catalyst volume (cc).
The above-mentioned catalyst for purifying an exhaust gas exhibits no
change in the performance thereof even when applied to an exhaust gas
containing carbon monoxide, hydrocarbons and hydrogen but not containing
an excessive amount of oxygen.
EXAMPLES
The present invention will now be further illustrated by, but is by no
means limited to, the following Examples.
COMPARATIVE EXAMPLE 1: PREPARATION OF COMPARATIVE CATALYST 1
A ZSM-5-like zeolite was synthesized according to the method described in
Example 5 of Japanese Unexamined Patent Publication (Kokai) No. 59-54620.
The zeolite had the following composition in terms of mole ratios of
oxides on an anhydrous basis:
1.1 Na.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.40 SiO.sub.2.
The zeolite was ion-exchanged with an aqueous ammonium chloride solution,
200 g of the resultant ammonium type ZSM-5 was put in 1800 ml of a 1.09
mol/liter aqueous lanthanum chloride solution, and the mixture was stirred
at 80.degree. C. for 16 hr. The stirred mixture was subjected to
solid-liquid separation, washed with water, subsequently put in 1800 ml of
a 0.23 mol/liter aqueous cobalt (II) acetate tetrahydrate solution, and
the mixture was stirred at 80.degree. C. for 16 hr. The slurry was
subjected to solid-liquid separation, the resultant zeolite cake was put
in a freshly prepared aqueous solution having the above-mentioned
composition, and the above-mentioned procedure was repeated. The slurry
was subjected to solid-liquid separation, washed with water, and dried at
110.degree. C. for 10 hr, to prepare a comparative catalyst 1. The
catalyst was subjected to a chemical analysis to determine the lanthanum
and cobalt contents, and as a result, it was found that the lanthanum and
cobalt contents were respectively 0.33 time, 1.13 times as divalent
cobalt, based on the number of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 1: PREPARATION OF CATALYST 1
A 15 g amount of comparative catalyst 1 prepared in Comparative Example 1
was put in 22 ml of a 0.025 mol/liter aqueous silver nitrate solution,
dried under reduced pressure while stirring, and further dried at
110.degree. C. for 16 hr, to thereby prepare a catalyst 1. The catalyst
was subjected to a chemical analysis to determined the contents of
lanthanum, cobalt and silver, and as a result, it was found that
lanthanum, cobalt and silver were contained in respective amounts of 0.33
time, 1.13 times as divalent cobalt and 0.1 time, based on the number of
moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 2: PREPARATION OF CATALYST 2
A 15 g amount of comparative catalyst 1 prepared in Comparative Example 1
was put in 43 ml of a 0.05 mol/liter aqueous silver nitrate solution,
dried under reduced pressure while stirring, and further dried at
110.degree. C. for 16 hr, to thereby prepare a catalyst 2. The catalyst
was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and silver, and as a result, it was found that
lanthanum, cobalt and silver were contained in respective amounts of 0.33
time, 1.13 times as divalent cobalt and 0.4 time, based on the number of
moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 3: PREPARATION OF CATALYST 3
A 15 g amount of comparative catalyst 1 prepared in Comparative Example 1
was put in 43 ml of a 0.05 mol/liter aqueous silver nitrate solution, and
the mixture was stirred at 80.degree. C. for 16 hr. The stirred mixture
was subjected to solid-liquid separation, washed with water, and dried at
110.degree. C. for 16 hr, to thereby prepare a catalyst 3. The catalyst
was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and silver, and as a result, it was found that
lanthanum, cobalt and silver were contained in respective amounts of 0.31
time, 1.05 times as divalent cobalt and 0.15 time, based on the number of
moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 4: PREPARATION OF CATALYST 4
A 20 g amount of ammonium type ZSM-5 prepared in Comparative Example 1 was
put in 180 ml of a 1.09 mol/liter aqueous lanthanum chloride solution, and
the mixture was stirred at 80.degree. C. for 16 hr. The stirred mixture
was subjected to solid-liquid separation, washed with water, subsequently
put in 180 ml of a 0.23 mol/liter aqueous cobalt (II) nitrate tetrahydrate
solution, and the mixture was stirred at 80.degree. C. for 16 hr. The
slurry was subjected to solid-liquid separation, the resultant zeolite
cake was put in a freshly prepared aqueous solution having the
above-mentioned composition, and the above-mentioned procedure was
repeated. The slurry was subjected to solid-liquid separation, washed with
water, and dried at 110.degree. C. for 10 hr, and the procedure of Example
2 was repeated to prepare a catalyst 4. The catalyst was subjected to a
chemical analysis to determine the contents of lanthanum, cobalt and
silver, and as a result, it was found that lanthanum, cobalt and silver
were contained respectively in amounts of 0.32 time, 0.42 time as divalent
cobalt and 0.4 time, based on the number of moles of Al.sub.2 O.sub.3 in
the zeolite.
COMPARATIVE EXAMPLE 2: PREPARATION OF COMPARATIVE CATALYST 2
A 200 g amount of ammonium type ZSM-5 prepared in Comparative Example 1 was
put in 1800 ml of a 1.09 mol/liter aqueous cerium chloride solution, and
the mixture was stirred at 80.degree. C. for 16 hr. The stirred mixture
was subjected to solid-liquid separation, washed with water, subsequently
put in 1800 ml of a 0.23 mol/liter aqueous cobalt (II) acetate
tetrahydrate solution, and the mixture was stirred at 80.degree. C. for 16
hr. The slurry was subjected to solid-liquid separation, the resultant
zeolite cake was put in a freshly prepared aqueous solution having the
above-mentioned composition, and the above-mentioned procedure was
repeated. The slurry was subjected to solid-liquid separation, washed with
water, and dried at 110.degree. C. for 10 hr, to thereby prepare a
comparative catalyst 2. The comparative catalyst was subjected to chemical
analysis to determine the contents of cerium and cobalt, and as a result,
it was found that cerium and cobalt were contained respectively in amounts
of 0.13 time and 1.12 times, as divalent cobalt, based on the number of
moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 5: PREPARATION OF CATALYST 5
A 15 g amount of comparative catalyst 2 prepared in Comparative Example 2
was put in 43 ml of a 0.05 mol/liter aqueous silver nitrate solution,
dried under reduced pressure while stirring, and further dried at
110.degree. C. for 16 hr, to thereby prepare a catalyst 5. The catalyst
was subjected to a chemical analysis to determine the contents of cerium,
cobalt and silver, and as a result, it was found that cerium, cobalt and
silver were contained in respective amounts of 0.13 time, 1.12 times as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 6: EVALUATION OF CATALYST ACTIVITY
Catalysts 1 to 5 and comparative catalysts 1 and 2 were each press-molded
and then crushed to regulate the size of granules to 12 to 20 meshes, and
an atmospheric fixed bed reaction tube was packed with 1 g of each of the
granular catalysts. The temperature of the catalyst bed was raised to
500.degree. C. while passing a gas having the following composition
(hereinafter referred to as "reaction gas") through the reaction tube at a
flow rate of 1000 ml/min, and the temperature was maintained at
500.degree. C. for 0.5 hr, to thereby conduct a pretreatment. Thereafter,
the temperature of the catalyst bed was raised from 300.degree. to
500.degree. C. In this case, the temperature was kept constant at each
50.degree. C. increment, to measure the catalytic activity at respective
temperatures. The NO.sub.x conversions at respective temperatures after
the state had become steady are shown in Table 1. The NO.sub.x conversion
can be determined by the following equation.
##EQU1##
wherein
NO.sub.x.sbsb.in =NO.sub.x concentration at inlet of fixed bed reaction
tube
NO.sub.x.sbsb.out =NO.sub.x concentration at outlet of fixed bed reaction
tube.
In all of the catalysts, little carbon monoxide was detected at 450.degree.
C. or above, and few hydrocarbons were detected at 400.degree. C. or
above.
Composition of reaction gas:
______________________________________
NO 700 ppm
O.sub.2 4%
H.sub.2 330 ppm
CO 1000 ppm
C.sub.3 H.sub.6
400 ppm
H.sub.2 O 3%
CO.sub.2 10%
N.sub.2 balance
______________________________________
TABLE 1
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
500.degree. C.
______________________________________
Cat- La Co Ag 11 34 61 48 37
alyst 1
Cat- La Co Ag 18 65 63 54 41
alyst 2
Cat- La Co Ag 13 46 62 50 36
alyst 3
Cat- La Co Ag 17 66 68 53 40
alyst 4
Cat- Ce Co Ag 12 49 53 43 35
alyst 5
Comp. La Co -- 6 31 49 39 28
Cat. 1
Comp. Ce Co -- 7 30 47 38 29
Cat. 2
______________________________________
EXAMPLE 7: EVALUATION OF DURABILITY OF CATALYSTS
Catalyst 1 and comparative catalyst 1 were subjected to an endurance
treatment at 800.degree. C. for 5 hr while flowing the above-mentioned
reaction gas therethrough, and then subjected to a measurement of the
catalytic activity in the same manner as that of Example 6. The NO.sub.x
conversions at respective temperatures after the state had become steady
are shown in Table 2.
TABLE 2
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
500.degree. C.
______________________________________
Cat- Co La Ag 9 27 45 50 40
alyst 1
Comp. Co La -- 5 25 43 38 31
Cat. 1
______________________________________
EXAMPLE 8: PREPARATION OF CATALYST 6
A 15 g amount of comparative catalyst 1 prepared in Comparative Example 1
was put in 43 ml of a 0.05 mol/liter aqueous nickel nitrate solution,
dried under a reduced pressure while stirring, and further dried at
110.degree. C. for 16, to thereby prepare a catalyst 6. The catalyst was
subjected to a chemical analysis to determine the contents of lanthanum,
cobalt and nickel, and as a result, it was found that lanthanum, cobalt
and nickel were contained in respective amounts of 0.33 time, 1.13 times
as divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 9: PREPARATION OF CATALYST 7
A 20 g amount of ammonium type ZSM-5 prepared in Comparative Example 1 was
put in 180 ml of a 1.09 mol/liter aqueous lanthanum chloride solution, and
the mixture was stirred at 80.degree. C. for 16 hr. The stirred mixture
was subjected to solid-liquid separation, washed with water, subsequently
put in 180 ml of a 0.23 mol/liter aqueous cobalt (II) nitrate tetrahydrate
solution, and the mixture was stirred at 80.degree. C. for 16 hr. The
slurry was subjected to solid-liquid separation, the resultant zeolite
cake was put in a freshly prepared aqueous solution having the
above-mentioned composition, and the above-mentioned procedure was
repeated. The slurry was subjected to solid-liquid separation, washed with
water, and dried at 110.degree. C. for 10 hr, and the procedure of Example
8 was repeated, to prepare a catalyst 7. The catalyst was subjected to a
chemical analysis to determine the contents of lanthanum, cobalt and
nickel, and as a result, it was found that lanthanum, cobalt and nickel
were contained respectively in amounts of 0.32 time, 0.42 time as divalent
cobalt and 0.4 time, based on the number of moles of Al.sub.2 O.sub.3 in
the zeolite.
EXAMPLE 10: PREPARATION OF CATALYST 8
A catalyst 8 was prepared in the same manner as that of Example 9, except
that nickel chloride was used instead of nickel nitrate. The catalyst was
subjected to a chemical analysis to determine the contents of lanthanum,
cobalt and nickel, and as a result, it was found that lanthanum, cobalt
and nickel were contained respectively in amounts of 0.32 time, 0.42 time
as divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 11: PREPARATION OF CATALYST 9
A catalyst 9 was prepared in the same manner as that of Example 9, except
that nickel acetate was used instead of nickel nitrate. The catalyst was
subjected to a chemical analysis to determine the contents of lanthanum,
cobalt and nickel, and as a result, it was found that lanthanum, cobalt
and nickel were contained respectively in amounts of 0.32 time, 0.42 time
as divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 12: PREPARATION OF CATALYST 10
A 15 g amount of comparative catalyst 2 prepared in Comparative Example 2
was put in 43 ml of a 0.05 mol/liter aqueous nickel nitrate solution,
dried under reduced pressure while stirring, and further dried at
110.degree. C. for 16, to thereby prepare a catalyst 10. The catalyst was
subjected to a chemical analysis to determine the contents of cerium,
cobalt and nickel, and as a result, it was found that cerium, cobalt and
nickel were contained in respective amounts of 0.13 time, 1.12 times as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
COMPARATIVE EXAMPLE 3: PREPARATION OF COMPARATIVE CATALYST 3
A comparative catalyst 3 was prepared in the same manner as that of
Comparative Example 2, except that yttrium was used as the rare earth
metal. The comparative catalyst was subjected to a chemical analysis to
determine the contents of yttrium and cobalt, and as a result, it was
found that yttrium and cobalt were contained in respective amounts of 0.28
time and 0.98 time, as divalent cobalt, based on the number of moles of
Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 13: PREPARATION OF CATALYST 11
A 15 g amount of comparative catalyst 3 prepared in Comparative Example 3
was put in 43 ml of a 0.05 mol/liter aqueous nickel nitrate solution,
dried under reduced pressure while stirring, and further dried at
110.degree. C. for 16, to thereby prepare a catalyst 11. The catalyst was
subjected to chemical analysis to determine the contents of yttrium,
cobalt and nickel, and as a result, it was found that yttrium, cobalt and
nickel were contained in respective amounts of 0.28 time, 0.98 time as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
COMPARATIVE EXAMPLE 4: PREPARATION OF COMPARATIVE CATALYST 4
A comparative catalyst 4 was prepared in the same manner as that of
Comparative Example 2, except that praseodymium was used as the rare earth
metal. The comparative catalyst was subjected to a chemical analysis to
determine the contents of praseodymium and cobalt, and as a result, it was
found that praseodymium and cobalt were contained in respective amounts of
0.14 time and 1.04 times, as divalent cobalt, based on the number of moles
of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 14: PREPARATION OF CATALYST 12
A 15 g amount of comparative catalyst 4 prepared in Comparative Example 4
was put in 43 ml of a 0.05 mol/liter aqueous nickel nitrate solution,
dried under reduced pressure while stirring, and further dried at
110.degree. C. for 16, to thereby prepare a catalyst 12. The catalyst was
subjected to chemical analysis to determine the contents of praseodymium,
cobalt and nickel, and as a result, it was found that praseodymium, cobalt
and nickel were contained in respective amounts of 0.14 time, 1.04 times
as divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
COMPARATIVE EXAMPLE 5: PREPARATION OF COMPARATIVE CATALYST 5
A 20 g amount of ammonium type ZSM-5 prepared in Comparative Example 1 was
put in 180 ml of a 0.23 mol/liter aqueous nickel acetate tetrahydrate
solution, and the mixture was stirred at 80.degree. C. for 16 hr. The
stirred mixture was subjected to solid-liquid separation, the resultant
zeolite cake was put in a freshly prepared aqueous solution having the
above-mentioned composition, and the above-mentioned procedure was
repeated. The slurry was subjected to solid-liquid separation, washed with
water, and dried at 110.degree. C. for 10 hr, to prepare a comparative
catalyst 5. The catalyst was subjected to a chemical analysis to determine
the nickel content, and as a result, it was found that nickel was
contained as divalent nickel in an amount of 1.40 times, based on the
number of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 15: PREPARATION OF CATALYST 13
A catalyst 13 was prepared in the same manner as that of Example 8, except
that zinc nitrate was used instead of nickel nitrate. The catalyst was
subjected to a chemical analysis to determine the contents of lanthanum,
cobalt and zinc, and as a result, it was found that lanthanum, cobalt and
zinc were contained in respective amounts of 0.33 time, 1.13 times as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 16: PREPARATION OF CATALYST 14
A catalyst 14 was prepared in the same manner as that of Example 9, except
that zinc nitrate was used instead of nickel nitrate. The catalyst was
subjected to a chemical analysis to determine the contents of lanthanum,
cobalt and zinc, and as a result, it was found that lanthanum, cobalt and
zinc were contained in respective amounts of 0.32 time, 0.42 times as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 17: PREPARATION OF CATALYST 15
A catalyst 15 was prepared in the same manner as that of Example 12, except
that zinc nitrate was used instead of nickel nitrate. The catalyst was
subjected to a chemical analysis to determine the contents of cerium,
cobalt and zinc, and as a result, it was found that cerium, cobalt and
zinc were contained in respective amounts of 0.13 time, 1.12 times as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 18: EVALUATION OF ACTIVITY OF CATALYST
Catalysts 6 to 15 and comparative catalysts 1 to 5 were subjected to a
measurement of the catalytic activity in the same manner as that of
Example 6. The NO.sub.x conversions at respective temperatures after the
state had become steady are shown in Table 3.
In all of the catalysts, little carbon monoxide was detected at 450.degree.
C. or above, and few hydrocarbons were detected at 400.degree. C. or
above.
TABLE 3
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
500.degree. C.
______________________________________
Cat- Co La Ni 11 43 54 42 32
alyst 6
Cat- Co La Ni 14 51 52 40 30
alyst 7
Cat- Co La Ni 10 37 50 41 30
alyst 8
Cat- Co La Ni 12 42 51 42 31
alyst 9
Cat- Co Ce Ni 13 49 51 41 30
alyst
10
Cat- Co Y Ni 12 50 52 42 32
alyst
11
Cat- Co Pr Ni 11 48 51 40 29
alyst
12
Cat- Co La Zn 8 33 58 50 41
alyst
13
Cat Co La Zn 7 16 60 49 39
alyst
14
Cat- Co Ce Zn 7 22 56 47 37
alyst
15
Comp. La Co -- 6 31 49 39 28
Cat. 1
Comp. Ce Co -- 7 30 47 38 29
Cat. 2
Comp. Co Y -- 6 29 48 37 27
Cat. 3
Comp. Co Pr -- 5 26 46 36 26
Cat. 4
Comp. -- -- Ni 10 31 36 32 28
Cat. 5
______________________________________
EXAMPLE 19: EVALUATION OF DURABILITY OF CATALYST
Catalysts 6 to 15 and comparative catalysts 1 to 5 were subjected to a
measurement of the durability in the same manner as that of Example 7. The
NO.sub.x conversions at respective temperatures after the state had become
steady are shown in Table 4.
TABLE 4
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
500.degree. C.
______________________________________
Cat- Co La Ni 9 32 53 58 50
alyst 6
Cat- Co La Ni 8 24 50 56 47
alyst 7
Cat- Co La Ni 6 23 48 59 49
alyst 8
Cat- Co La Ni 6 22 45 48 41
alyst 9
Cat- Co Ce Ni 7 24 50 54 43
alyst
10
Cat- Co Y Ni 7 21 47 50 41
alyst
11
Cat- Co Pr Ni 6 21 48 53 42
alyst
12
Cat- Co La Zn 7 24 45 44 38
alyst
13
Cat- Co La Zn 6 20 40 42 38
alyst
14
Cat- Co Ce Zn 6 19 41 43 39
alyst
15
Comp. La Co -- 6 31 49 39 28
Cat. 1
Comp. Ce Co -- 7 30 47 38 29
Cat. 2
Comp. Co Y -- 5 23 40 36 29
Cat. 3
Comp. Co Pr -- 4 22 39 35 27
Cat. 4
Comp. -- -- Ni 2 7 21 32 28
Cat. 5
______________________________________
EXAMPLE 20: PREPARATION OF CATALYST 16
A 15 g amount of comparative catalyst 1 prepared in Comparative Example 1
was put in 43 ml of a 0.05 mol/liter aqueous tetraaminedichloroplatinum
solution, dried under a reduced pressure while stirring, and further dried
at 110.degree. C. for 16 hr, to thereby prepare a catalyst 16. The
catalyst was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and platinum, and as a result, it was found that
lanthanum, cobalt and platinum were contained in respective amounts of
0.33 time, 1.13 times as divalent cobalt and 0.4 time, based on the number
of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 21: PREPARATION OF CATALYST 17
A 15 g amount of comparative catalyst 1 prepared in Comparative Example 1
was put in 22 ml of a 0.025 mol/liter aqueous tetraaminedichloroplatinum
solution, dried under a reduced pressure while stirring, and further dried
at 110.degree. C. for 16 hr, to thereby prepare a catalyst 17. The
catalyst was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and platinum, and as a result, it was found that
lanthanum, cobalt and platinum were contained in respective amounts of
0.33 time, 1.13 times as divalent cobalt and 0.1 time, based on the number
of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 22: PREPARATION OF CATALYST 18
A 200 g amount of ammonium type ZSM-5 prepared in Comparative Example 1 was
put in 1800 ml of a 1.09 mol/liter aqueous lanthanum chloride solution,
and the mixture was stirred at 80.degree. C. for 16 hr. The stirred
mixture was subjected to solid-liquid separation, washed with water,
subsequently put in 1800 ml of a 0.23 mol/liter cobalt (II) nitrate
tetrahydrate solution, and the mixture was stirred at 80.degree. C. for 16
hr. The slurry was subjected to solid-liquid separation, the resultant
zeolite cake was put in a freshly prepared aqueous solution having the
above-mentioned composition, and the above-mentioned procedure was
repeated. The slurry was subjected to solid-liquid separation, washed with
water, and dried at 110.degree. C. for 20 hr, to prepare ZSM-5 containing
cobalt and lanthanum. 15 g of the ZSM-5 containing cobalt and lanthanum
was put in 43 ml of a 0.05 mol/liter aqueous tetraaminedichloroplatinum
solution, dried under a reduced pressure while stirring, and further dried
at 110.degree. C. for 16 hr, to thereby prepare a catalyst 18. The
catalyst was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and platinum, and as a result, it was found that
lanthanum, cobalt and platinum were contained in respective amounts of
0.32 time, 0.42 time as divalent cobalt and 0.4 time, based on the number
of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 23: PREPARATION OF CATALYST 19
A 15 g amount of the ZSM-5 containing cobalt and lanthanum prepared in
Example 22 was put in 43 ml of a 0.05 mol/liter aqueous manganese acetate
solution, dried under a reduced pressure while stirring, and further dried
at 110.degree. C. for 16 hr, to thereby prepare a catalyst 19. The
catalyst was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and manganese, and as a result, it was found that
lanthanum, cobalt and manganese were contained in respective amounts of
0.32 time, 0.42 time as divalent cobalt and 0.4 time, based on the number
of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 24: PREPARATION OF CATALYST 20
A catalyst 20 was prepared in the same manner as that of Example 23, except
that manganese nitrate was used instead of manganese acetate. The catalyst
was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and manganese, and as a result, it was found that
lanthanum, cobalt and manganese were contained in respective amounts of
0.32 time, 0.42 time as divalent cobalt and 0.4 time, based on the number
of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 25: PREPARATION OF CATALYST 21
A catalyst 21 was prepared in the same manner as that of Example 23, except
that manganese chloride was used instead of manganese acetate. The
catalyst was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and manganese, and as a result, it was found that
lanthanum, cobalt and manganese were contained in respective amounts of
0.32 time, 0.42 time as divalent cobalt and 0.4 time, based on the number
of moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 26: PREPARATION OF CATALYST 22
A 15 g amount of comparative catalyst 2 prepared in Comparative Example 2
was put in 43 ml of a 0.05 mol/liter aqueous tetraaminedichloroplatinum
solution, dried under a reduced pressure while stirring, and further dried
at 110.degree. C. for 16 hr, to thereby prepare a catalyst 22. The
catalyst was subjected to a chemical analysis to determine the contents of
cerium, cobalt and platinum, and as a result, it was found that cerium,
cobalt and platinum were contained in respective amounts of 0.13 time,
1.12 times as divalent cobalt and 0.4 time, based on the number of moles
of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 27: PREPARATION OF CATALYST 23
A catalyst 23 was prepared in the same manner as that of Example 26, except
that manganese nitrate was used instead of tetraaminedichloroplatinum. The
catalyst was subjected to a chemical analysis to determine the contents of
cerium, cobalt and manganese, and as a result, it was found that cerium,
cobalt and manganese were contained in respective amounts of 0.13 time,
1.12 times as divalent cobalt and 0.4 time, based on the number of moles
of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 28: EVALUATION OF ACTIVITY OF CATALYSTS
Catalysts 16 to 22 were pretreated in the same manner as that of Example 6,
and the temperature of the catalyst bed was raised from 250.degree. to
450.degree. C. In this case, the temperature was kept constant at each
50.degree. C. increment to measure the catalytic activity at respective
temperatures. The NO.sub.x conversions at respective temperatures after
the state had become steady are shown in Table 5.
TABLE 5
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
250.degree. C.
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
______________________________________
Cat- Co La Pt 41 34 30 19 10
alyst
16
Cat- Co La Pt 38 23 19 14 9
alyst
17
Cat- Co La Pt 36 28 23 14 9
alyst
18
Cat- Co La Mn 18 40 51 44 34
alyst
19
Cat- Co La Mn 18 33 52 40 32
alyst
20
Cat- Co La Mn 15 25 48 45 35
alyst
21
Cat- Co Ce Pt 40 34 29 18 10
alyst
22
Cat- Co Ce Mn 18 35 52 43 35
alyst
23
Comp. La Co -- 6 31 49 39 28
Cat. 1
Comp. Ce Co -- 7 30 47 38 29
Cat. 2
______________________________________
In the comparative catalysts, little carbon monoxide was detected at
450.degree. C. or above, and few hydrocarbons were detected at 400.degree.
C. or above. On the other hand, in the catalysts of examples of the
present invention, little carbon monoxide was detected at 400.degree. C.
or above, and few hydrocarbons were detected at 350.degree. C. or above.
EXAMPLE 29: EVALUATION OF DURABILITY OF CATALYSTS
Catalysts 16 to 22 were pretreated in the same manner as that of Example 7,
and the catalytic activity was measured in the same manner as that of
Example 28. The NO.sub.x conversions at respective temperatures after the
state had become steady are shown in Table 6.
TABLE 6
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
250.degree. C.
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
______________________________________
Cat- Co La Pt 37 36 27 17 9
alyst
16
Cat- Co La Pt 24 29 21 13 8
alyst
17
Cat- Co La Pt 43 36 25 17 10
alyst
18
Cat- Co La Mn 10 12 34 41 38
alyst
19
Cat- Co La Mn 10 13 33 40 39
alyst
20
Cat- Co La Mn 10 16 35 41 40
alyst
21
Cat- Co Ce Pt 37 33 28 16 10
alyst
22
Cat- Co Ce Mn 10 14 34 40 38
alyst
23
Comp. La Co -- 6 31 45 39 28
Cat. 1
Comp. Ce Co -- 7 30 47 38 29
Cat. 2
______________________________________
EXAMPLE 30: PREPARATION OF CATALYST 24
A 200 g amount of ammonium type ZSM-5 prepared in Comparative Example 1 was
put in 1800 ml of a 1.09 mol/liter aqueous lanthanum chloride solution,
and the mixture was stirred at 80.degree. C. for 16 hr. The stirred
mixture was subjected to solid-liquid separation, washed with water,
subsequently put in 1800 ml of a 0.23 mol/liter cobalt (II) nitrate
tetrahydrate solution, and the mixture was stirred at 80.degree. C. for 16
hr. The slurry was subjected to solid-liquid separation, the resultant
zeolite cake was put in a freshly prepared aqueous solution having the
above-mentioned composition, and the above-mentioned procedure was
repeated. The slurry was subjected to solid-liquid separation, washed with
water, and dried at 110.degree. C. for 20 hr, to prepare ZSM-5 containing
cobalt and lanthanum. Then, 15 g of the ZSM-5 containing cobalt and
lanthanum was put in 43 ml of a 0.05 mol/liter aqueous copper acetate
solution, dried under a reduced pressure while stirring, and further dried
at 110.degree. C. for 16 hr, to thereby prepare a catalyst 24. The
catalyst was subjected to a chemical analysis to determine the contents of
lanthanum, cobalt and copper, and as a result, it was found that
lanthanum, cobalt and copper were contained in respective amounts of 0.32
time, 0.42 time as divalent cobalt and 0.4 time, based on the number of
moles of Al.sub.2 O.sub.3 in the zeolite.
EXAMPLE 31: PREPARATION OF CATALYST 25
A catalyst 25 was prepared in the same manner as that of Example 30, except
that rhodium nitrate was used instead of copper acetate. The catalyst was
subjected to a chemical analysis to determine the contents of lanthanum,
cobalt and rhodium, and as a result, it was found that lanthanum, cobalt
and rhodium were contained in respective amounts of 0.32 time, 0.42 time
as divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 32: PREPARATION OF CATALYST 26
A 15 g amount of comparative catalyst 2 prepared in Comparative Example 2
was put in 43 ml of a 0.05 mol/liter aqueous copper nitrate solution,
dried under a reduced pressure while stirring, and further dried at
110.degree. C. for 16 hr, to thereby prepare a catalyst 26. The catalyst
was subjected to a chemical analysis to determine the contents of cerium,
cobalt and copper, and as a result, it was found that cerium, cobalt and
copper were contained in respective amounts of 0.13 time, 1.12 times as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 33: PREPARATION OF CATALYST 27
A catalyst 27 was prepared in the same manner as that of Example 32, except
that rhodium nitrate was used instead of copper nitrate. The catalyst was
subjected to a chemical analysis to determine the contents of cerium,
cobalt and rhodium, and as a result, it was found that cerium, cobalt and
rhodium were contained in respective amounts of 0.13 time, 1.12 time as
divalent cobalt and 0.4 time, based on the number of moles of Al.sub.2
O.sub.3 in the zeolite.
EXAMPLE 34: EVALUATION OF ACTIVITY OF CATALYSTS
The catalytic activities of catalysts 24 to 27 were measured in the same
manner as that of Example 28. The NO.sub.x conversions at respective
temperatures after the state had become steady are shown in Table 7.
In all of the catalysts, little carbon monoxide was detected at 450.degree.
C. or above, and few hydrocarbons were detected at 400.degree. C. or
above.
TABLE 7
______________________________________
Cat- NO.sub.x conversion (%)
alyst Composition
250.degree. C.
300.degree. C.
350.degree. C.
400.degree. C.
450.degree. C.
______________________________________
Cat- Co La Cu 25 35 48 36 28
alyst
24
Cat- Co La Rh 20 25 20 19 15
alyst
25
Cat- Co Ce Cu 26 35 46 37 30
alyst
26
Cat- Co Ce Rh 20 23 20 18 16
alyst
27
Comp. La Co -- 6 31 49 39 28
Cat. 1
Comp. Ce Co -- 7 30 47 38 29
Cat. 2
______________________________________
As apparent from Tables 1 to 7, the catalysts of the present invention are
superior to the comparative catalysts in the capability thereof of
purifying an exhaust gas containing an excessive amount of oxygen, in
particular, the capability of removing nitrogen oxides.
Specifically,
1) the addition of silver to cobalt and a rare earth metal contributes to
an improvement in the capability of removing nitrogen oxides,
2) the addition of nickel and/or zinc to cobalt and a rare earth metal
contributes to an improvement in the capability of removing nitrogen
oxides at a high temperature of 350.degree. C. or above,
3) the addition of platinum and/or manganese to cobalt and an alkaline
earth metal contributes to an improvement in the capability of removing
nitrogen oxides at a low temperature of 350.degree. C. or below, and
4) the addition of copper and/or rhodium to cobalt and a rare earth metal
contributes to a slight improvement in the capability of removing nitrogen
oxides at a low temperature.
Therefore, nitrogen oxides, carbon monoxide and hydrocarbons can be removed
with a high conversion by bringing the catalyst of the present invention
into contact with an exhaust gas, even when the exhaust gas contains an
excessive amount of oxygen.
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